Modern vehicle designs place an increasing demand for improved smooth running and driving comfort. To meet these requirements, there has been an increasing demand for further improved vibration damping or isolating characteristics of the engine mount. Minimizing the transmission of engine vibration at the bounce resonance frequency, i.e., the resonance frequency where the engine bounces most vigorously, to the frame is of particular interest, since it greatly impacts the smoothness of the ride comfort.
It is well known in the industry that the engine bounce frequency is a result of the body/engine properties. Thus for every change in the design of the body/engine (and hence the bounce resonance frequency), a new mount has to be designed.
A variety of engine mount assemblies are presently in use in the automotive industry to reduce the transmission of engine vibration to the car body. Examples of such vibration damping and/or isolation devices are vibration-absorbing, elastomeric automotive engine mounts. Hydraulic mounts combine the properties of elastomeric materials and viscous dampening properties of non-compressible hydraulic fluids and have been used in automobiles for decades. Hydraulic mounts are commonly elastomeric engine mounts enclosing a fluid-containing cavity. The cavity is separated into two chambers by a dividing plate where the plate contains an orifice to allow fluid to communicate between the two chambers. A pressure-receiving fluid chamber is formed between the orifice or partition plate and an elastic mount body, whereas an equilibrium chamber is formed between the plate and a diaphragm. These mounts are referred to as passive mounts (i.e., the dampening characteristics of which are a function of the design only).
Active mounts have more recently become known in the art. They provide electronic control of their dampening characteristics/behavior, and can typically exhibit responsive dampening behavior based on electronic input signals.
Active controllable dampening behavior of hydraulic mounts can be achieved by employing an electronically variable gate or valve to the orifice or track between the aforementioned fluid chambers. As the flow rate of fluid that is communicated between the chambers is altered, the dampening stiffness of the mount varies accordingly. The slow response time of mechanical valves or gates makes them less ideal for use in realtime tunable damping systems.
More recently, the use of controllable fluids such as electrorheological (ER) and magnetorheological (MR) fluids has been applied in engine mount designs. Examples of the use of MR hydraulic fluid dampers can be found in U.S. Pat. Nos. 5,284,330; 5,878,850 and 5,712,783. One example of an ER fluid mount can be found in U.S. Pat. No. 4,733,758. Magnetorheological fluids are materials that respond to an applied magnetic field with a dramatic change in the rheological behavior. The essential characteristic of these fluids is their ability to reversibly change from a free-flowing, linear, viscous liquid to a semisolid with controllable yield strength in milliseconds when exposed to a magnetic field. In MR engine mounts, the MR fluid is communicated via flow apertures in the separating plate between the two chambers where the fluid is exposed to a controllable magnetic field. As the MR fluid is exposed to the magnetic field, its sheer resistance increases and the dampening stiffness of the mount increases accordingly.
Active hydraulic MR mounts can be controlled by a current signal producing a proportional electromagnetic field in the track between the fluid chambers. The control signal is commonly produced by a controller unit utilizing one or more electrical control input signals. Typically, a sensor signal that is received by the controller will be proportional to a parameter such as vibratory motion (such as relative displacement, velocity or acceleration), but a sensor that measures mount fluid pressure, or other sensed dynamic properties can also be used. In complex control systems where the controller processes several such input signals to generate an output signal, the performance of the mount will depend greatly on the design and calibration of the system.
The use of MR and ER fluids in vibration damping mounts enables such mounts to produce real-time varying damping characteristics in response to supplied real-time control signals. It is well known in the art that successful damper performance for any vibration damping system is greatly dependent upon the particular control algorithm employed to vary the damper forces. Successful active damping of suspension systems and engine mounts in vehicles will typically require the controller to process several input signals from sensors such as relative displacement and/or its derivatives (velocity/acceleration), external force system disturbances and the like. One such control algorithm is presented in U.S. Pat. No. 4,953,089. Other examples of control algorithms for active vibration attenuation can be found in U.S. Pat. Nos. 3,807,678; 4,491,207; 5,712,783; 3,807,678 and 4,491,207 and references therein.
In designing such a control system, appropriate sensory input to the controller must be determined as well as the design of the control structure that is to be implemented in the controller device. An example of a controllable damper system and references to related patents can be found in U.S. Pat. No. 5,712,783.
It would be advantageous to provide a control system and method with the capability to control vibrations of various engine/frame assemblies without redesigning the system.